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<br />. <br /> <br />12 <br /> <br />. <br /> <br />falling particles created downdraft, and the seeding technique brought <br /> <br /> <br />uncertainty in the starting time of growth. However, additional difficulties <br /> <br /> <br />existed which include the development of polycrystallines below -150C and <br /> <br /> <br />the difficulties measuring the smallest dimension of thin plates and columns. <br /> <br /> <br />Despite these problems, proper analysis of the data and, then, careful <br /> <br /> <br />comparison with others helped make use of them for present purpose. <br /> <br />. <br /> <br />. <br /> <br />Ryan. Wishart and Shaw (J 976) <br /> <br /> <br />A chamber, 1.8 m high and 4.5 m3 in volume, contained supercooled fog <br /> <br /> <br />that was generated by means of a heated vapor source at the base. Inside the <br /> <br /> <br />chamber, two thermocouples, centrally placed one-third and two-thirds up <br /> <br /> <br />from the base, monitored the temperature, and they never differed by more <br /> <br /> <br />than 0.50C. By measuring the droplet size distribution and the number <br /> <br /> <br />concentration, an axially scattering cloud droplet spectrometer provided the <br /> <br /> <br />means for determining the liquid water content. <br /> <br /> <br />After the fog achieved equilibrium, ice nucleation took place inside a <br /> <br /> <br />syringe by popping a small polyethylene bubble that prevented the <br /> <br /> <br />contamination of the chamber and the introduction of strong local thermal <br /> <br /> <br />gradients. Also, this technique controlled the amount of activated nucleants <br /> <br /> <br />entering into the chamber and thus allowed the crystal concentration to be <br /> <br /> <br />within the range of 5 - 20 an". As the ice crystal grew, the fog maintained a <br /> <br /> <br />liquid water content of 1 to 1.5 glm' except at -15 and -l7"C where the content <br /> <br /> <br />was kept at approximately 3 g/m'. The high concentration ensured that the <br /> <br /> <br />cloud droplet to ice crystal ratio was always greater than 5:1. Ryan, Wishart <br /> <br />and Holroyd (1974) reported that the growth rate was not affected by this ratio <br /> <br /> <br />provided that this quantity was greater than 5:1 and, thus, implied that the <br /> <br /> <br />water vapor was not exhausted to a pressure below water saturation. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />. <br />